Perpendicular recording has been developed in part to achieve higher recording density than is realized with longitudinal recording devices. A PMR write head typically has a main pole layer with a small surface area at an ABS, and coils that conduct a current and generate a magnetic flux in the main pole that exits through a write pole tip and enters a magnetic media (disk) adjacent to the ABS. The flux may return through a shield structure to the back gap region which connects the main pole with the shield structure. A trailing write shield on the write gap above the main pole and along the ABS is employed in a PMR trailing shield writer and has been used to replace the monopole writer due to its excellent down-track field gradient which provides a better signal-to-noise ratio from the better written transition quality. However, the trailing shield writer has issues which require additional design optimization. For example, there is return field induced partial erasure (RFPE) that is caused by excessive return field near the trailing shield seed layer, mainly on track as described by Bai et al. in “Return field induced partial erasure in perpendicular recording using trailing edge shielded writers”, IEEE Trans. Magn., Vol. 43, pp 600-604 (2007). Another concern is that a trailing shield may cause adjacent track erasure (ATE) or wide area track erasure (WATE) which are often related to excessive flux being delivered to the shields on the ABS through the trailing shield (PP3) path.
Perpendicular magnetic recording has become the mainstream technology for disk drive applications beyond 150 Gbit/in2. The demand for improved performance drives the need for a higher areal density which in turn calls for a continuous reduction in transducer size. A PMR head which combines the features of a single pole writer and a double layered media (magnetic disk) has a great advantage over LMR in providing higher write field, better read back signal, and potentially much higher areal density. Typically, today's magnetic head consists of a writer and a reader as separate elements that are formed adjacent to one another along an ABS. The read head may be based on a TMR element in which a tunnel barrier layer separates two ferromagnetic (FM) layers where a first FM layer has a fixed magnetization direction and the second FM layer has a magnetic moment that is free to rotate about a direction orthogonal to the direction of the magnetic moment in the reference “fixed” layer. The resistance across the barrier changes as the free layer moment is rotated. This signal is used to detect the small magnetic field from the recorded magnetization pattern on the media.
Reducing the magnetic spacing from read/write heads to the magnetic media during both writing and reading is the most important factor in achieving better performance in high density recording. The writer and reader are separated by several microns in a typical recording head and are made of several different materials each having a unique coefficient of thermal expansion (CTE). Therefore, the protrusion of the reader and writer are usually quite different due to the effect of varying operating temperatures, applying dynamic flying height (DFH) power to actuate the reader or writer, or from write current excitation. The ratio of reader protrusion rate/writer protrusion rate is called the gamma ratio. A low gamma ratio significantly below 1 means the writer protrusion rate is much higher than the reader protrusion rate, and could potentially put a greater limit to achievable reader spacing. Improvements in PMR head design are needed to control the writer protrusion distance.
Recent efforts have involved improving the saturation speed of a PMR writer by enlarging the back gap and thus allowing more flux through the larger back gap. Unfortunately, as shown in FIG. 1, the ATE and WATE become significantly worse which is indicated by comparing the ATE of a standard head in the (a) diagram with ATE in a head (b) having an enlarged back gap. An improved head design is needed to take advantage of better saturation speed without compromising ATE performance.
Referring to FIGS. 2a, 2b, two prior art PMR writers are depicted. In FIG. 2a, the PP3 layer 27 has a height h1 at the ABS 30-30 that is defined by the ABS lapping process. PP3 refers to a top portion of the trailing shield that includes the entire portion of the trailing shield formed above a plane that is approximately coplanar with a top surface of the top yoke 22. Therefore, the PP3 thickness h1 at the ABS is much larger than the plated PP3 thickness p in other regions due to the dome shape of the photoresist layer 26 that covers the coils 25. Other layers pictured in the PMR writer are a substrate 20, main pole layer 21 with write pole tip 21p and tapered trailing side 21t, top yoke 22, dielectric layer 23 with write gap 23g, first write shield 24, and overcoat layer 28. Even though the photoresist layer 26 is recessed farther from the ABS 30-30 in FIG. 2b, the thickness h2 of the PP3 layer 27 at the ABS is still equivalent to the plated PP3 thickness p in other regions. As a result, neither configuration is designed to limit the flux flowing from the PP3 trailing shield section to the vicinity of the trailing edge 21t of the main pole during normal writing which means the ATE/WATE performance is not improved.
Another disadvantage of having a large amount of metal in the PP3 layer along the ABS is that the metal serves as a heat sink and leads to a large pole trip protrusion (PTP) which in turn limits the budget for the read/write head spacing from the media and thereby degrades read/write performance.
A search of the prior art revealed the following references that relate to the effect of a trailing write shield design on flux choking.
U.S. Pat. No. 7,538,976 discloses a trailing shield with a specially configured back edge opposite the ABS where a center portion has a constant throat height (TH) while first and second intermediate positions have a greater TH than the center portion. The structure chokes off stray fields that might be picked up by outer portions of the shield to prevent excessive flux from reaching the center portion where it may affect writing.
In U.S. Patent Application No. 2009/0091862, a tapered main pole is described with integrated side and tailing shields to eliminate flux choking at the side and trailing shield interface.
None of the prior art references solve the issue of improved control for pole tip protrusion while simultaneously providing flux choking from the trailing shield which is necessary to meet the performance requirements of advanced PMR writers.